Sets of chemical elements

The chemical elements are subdivided into sets on the periodic table. Each element of one set has similar characteristics with the others. There are following nsets:

Alkali Metals

The alkali metals are the 6 elements in the group 1 of the periodic table. They would be lithium, sodium, potassium, rubidium, cesium and francium. The name “alkali metals” comes from the fact that they react with water and form alkalis (strong bases neutralizing acids). Most alkali metals are very rare, although two of them, sodium and potassium, are very common.

They are highly reactive and are usually found combined with other elements. Their reactions are often very violent. They are rarely found as pure elements in the nature. Francium is a natural radioactive isotope and it’s so rare that it wasn’t known until 1939.

Some of the main characteristics of the alkali metals are the silver-like lustre, the high ductility and the very high conductivity of electricity and heat, similar to the ones of the other metals. They also have low melting points. Lithium, one of the alkali metals, is the lightest known metal. They also tend to change into ions when they react with non-metals. This causes the compounds of alkali metals and non-metals to have a high melting point. They react very good with the nonmetals, because of their electropositivity. They oxidate easier than other metals and their reactions with water are often violent. They also react with other non-metals.

They are often used industrially. Sodium is the most used for industry. Many substances, like salt, baking powder, etc. contain sodium. It is also used as a heat-conducting fluid in nuclear reactors. Another widely used alkali metal is lithium. It is very useful, because of it’s low weight. Alloys are made with it. Another very known example are the lithium batteries.

Alkine-earth Metals

The alkaline-earth metals are 6 metals of the group 2. Their names are beryllium, magnesium, calcium, strontium, barium and radium. They are very similar to the metals of the group 1, the alkali metals. They easily lose electrons and become cations. The oxides resulting after reactions are basic (= alkaline = not acidic), although it varies. Beryllium oxide is more amphoteric (reactive with both acids and bases), whereas barium oxide is strongly basic. They are also highly reactive, e.g. magnesium reacts very violently with oxygen.

All alkaline-earth metals have a commercial use, except radium, which is highly radioactive. Magnesium is used e.g. in sports, while calcium is used e.g. in medical industry.

Alkaline-earth metals are very good conductors. They also have a very light gray color when they are freshly cut. They aren’t necessarily all hard, some of them are barely harder than lead. Their melting and boiling points are harder than the ones of the alkali metals. Their atoms have similar structures and all of them easily become ions. Similar to the alkali metals, they form compounds by having valens electrons, electrons shared by two atoms, there are exceptions though.

Halogens

Halogens are the 6 nonmetallic elements in the group 17. The elements are fluorine, chlorine, borine, iodine, astatine and tennessine. Their name comes from Greek hal- (salt) and -gen (producing), since they all form sodium salts compounds, the best known is table salt, sodium chloride. Because of their high reactivity, halogens are not found as pure elements in nature. Fluorine is the most common, while astatine and tennessine can’t be found in the nature, since they are short-lived radioactive isotopes. Halogens are very similar to each other, and their compounds also have similar properties. There are however, some differences between the halogen elements. The most reactive of them is fluorine.

Chlorine is the best known halogen element. It is widely used to purify water in pools. Table salt is also a well-known compound. Fluoride is often added to water to prevent tooth decay, but it is also used in e.g. refrigerators. Iodine is widely known for its anti-sceptic usage.

The halogens are oxidizing agents, which means they raise the state of oxidation by moving electrons easily. The oxidation is the reaction of oxygen with another element. But halogens themselves can combine with other elements, forming halides, i.e. fluorides, chlorides, etc. Many of them are considered to be salts corresponding with the respective hydrogen halides, colourless gases at room temperature and (except hydrogen fluoride) strong acids if they are in aqueous solutions. The term salt is actually derived from the actual table salt, which is, like already mentioned, sodium chloride. Fluorides are usually more stable and consequently with a higher tendency than the other halides. Exactly like the alkali and alkaline-earth metals they form compounds by sharing an electron.

Noble Gases

The noble gases are the chemical elements that make up the group 18 of the periodic table. The corresponding elements are helium, neon, argon, krypton, xenon, radon and oganesson. They were labeled as the group 0 in the past, since it was believed they can’t form compounds with other atoms. However, after it was discovered that they indeed can form compounds, the group received the designation “group 18”. It was also thought that they are very rare, although after years of research scientists found out that they are very abundant on the Earth and in the universe. All of them are available in the Earth’s atmosphere. The bigger their atomic number, the less common the elements are. Helium is the second most frequent element in the universe, after hydrogen. Radon is highly radioactive and is the decomposition of radium compounds. The radon nuclei constantly emit alpha particles (helium nuclei) and energy.

Their typical characteristics are that they are colourless, tasteless, odourless and nonflammable. They also barely react with others, which make them perfect for usage for creating unreactive environments for operations like cutting, welding and refining of metals. They absorb and emit electromagnetic radiation in a less complex way than other substances. On the periodic table, they are placed between the most electronegative elements, the halogens, and the most electropositive, the alkali metals. Only 3 of them, krypton, xenon and radon, have known stable compounds. The compounds are powerful oxidizing agents.

Lanthanoids

Lanthanoids are 15 consecutive elements on the periodic table, form lanthanum to lutetium. They form the rare-earth elements group with the two elements scandium and yttrium. Their atoms have similar properties and behaviour, the most frequent valences being 3 or 4. The elements are more often called lanthanides, but the International Union of Pure and Applied Chemistry recommends the name lanthanoid, since names ending in -ide are usually used for anions.

Actinoids

Actinoids, or actinides, are 15 consecutive elements on the periodic table, from actinium to lawrencium. All of them are radioactive, and the best-known is uranium. Although several occur natiurally, like uranium, most of them are man-made. Two of them, uranium and plutonium, have been used in nuclear weapons. The nuclear bombs thrown over Japan during the Second World War killed hundreds of thousands of people. Like lathanoids, the wrong name (actinides) is used more often than the name recommended by the IUPAC (actinoids).

4 actinoids occur naturally, namely actinium, protactinium and uranium. The remaining actinoids are all man-made through bombardments of the naturally occuring actinoids with neutrons or heavy ions in particle accelerators. They usually do not occur in nature, since they decay really fast. But there are some very rare exceptions. Since all actinoids are heavy metals, they are toxic for our body, and they are also raqdiactive, which causes mutation and can cause cancer.

Transition Metals

The transition metals are the group of metals that have valence electrons in two shells instead of only one. The term "transition" has no chemical meaning. They occupy the middle of the periodic table. As their name already tells us, they are metals, and many of them are hard and lustrous with high melting and boiling points. Many of the transition metals are commercially important, e.g. titanium, iron, nickel, copper, etc. They also form useful alloys with other metals. Some of them, such as platinum, silver and gold, are also noble. That means they are immune to simple acids.

All transition metals form stable compounds with only some exceptions. The lanthanoids and actinoids are theoretically also transition metals, but they differ from the rest through for example not forming stable compounds.

They are subdivided into three groups, according to their electronic structures, the first, second and third transition series

Several transition metals are important for living creatures, e.g. the humans. Many living beings need transition metals like iron, cobalt and copper, of which iron is the most important. It participates in the processes of oxygen transport and electron transfer

Metals

Metals are all the elements that are characterized by high electrical and thermal conductivity as well as other properties like malleability, ductibility and high reflectivity. The already described alkali metals, transition metals and alkaline-earth metals are also metals, there are also the metalloids and the metals with no further subdivision like gallium or lead.

Metals are usually solids at room temperature (there is one exception, mercury) and have a crystalline forms. In most cases they have a simple crystal structure distinguished by close packed antoms and being highly symmetric. Another typicasl feature of metal atoms is that they contain less than half of the full complement of electrons in their outermost shell. This causes many metals to not form compounds with each other, although they often form compounds with nonmetals like oxygen through valence electrons. Metals have big differences in their chemical reactivity. Some like gold and silver have low reactivity, while others like lithium react very easily and violently.

The high conductivity of the non-transition metals are explained by the free-electron theory. According to this theory do the metals lose their valence electron to the entire solid. This rises the thermal and electrical conductivity of the whole entity. The conductivity of the transition metals is explained by the band theory. This theory takes account not only of free valence electrons, but also so called d electrons. These electrons have a different orbital than the others (s, p and f). Each orbital has different energies.

Metalloids

Metalloid is the imprecise term used to describe elements that have properties typical for metals and for nonmetals. The typical metalloids are boron, silicon, germanium, arsenic, antimony, tellurium and probably also bismuth, polonium and astanite. All these elements are found near the center of the main block of the periodic table. There are no properties that can tell with certainity if an element is a metalloid. Since most metalloids display semiconducting properties, people sometimes also include gray silicon, which, unlike white silicon, is rather a semicinductor than a metal, and also graphite carbon, which is, unlike diamond, rather a semimetal than an insulator. Metalloids have an intermediate electronegativity and can also form compounds.

Nonmetals

Nonmetals are elements with a finite activation energy. Consequently, nonmetals are either insulators or semiconductors. They have breakdowns if they are exposed to high voltages or high temperatures. Nonmetals can be found in solid, liquid or gaseous forms. However, unlike metals, they have both mechanical and optical differences between each other.

Chemically, nonmetals are divided in two groups: the covalent and ionic nonmetals. Covalent nonmetals have atoms with small sizes, high electronegativities, low valence vacancy and tend to form negative ions in chemical reactions. Ionic metals however have both small and large atoms and form both negative or positive ions.